When you first start the game,you'll be in your room.Exit the room and go out of the house.Then,go up the road to Viridian City.You'll be stopped by Professor Oak.He'll lead you to his lab and tell you to pick a Pokemon.After you pick a Pokemon,your rival will challenge you to a battle.Beat him to get experience points.
Now,make your way to Viridian City.Go into the Pokemon Mart to get Oak's parcel.Deliver it to him and get your Pokedex and the right to move on.When you get to Viridian Forest,you should have Pokemon that are between levels 6-13.After you get through it,battle the gym leader to get the Boulder Badge.
Now,go to Mt.Moon.You'll meet with Team Rocket there,so prepare your Pokemon.After you beat them,you'll get to choose between 2 fossils used to clone Pokemon.Pick which ever one you want and move on.
You'll come to Cerulean City now.Go up the bridge and battle your rival.Defeat him and continue to battle 5 other trainers to get a nugget.When you reach Bill's house,help him turn himself back to a human.You'll be rewarded with a S.S.Anne ticket.
Go through the Underground Tunnel to reach Vermillion City.Use your S.S.Anne ticket to get on the ship.You'll meet your rival at the entrance to the captain's room.Beat him and help the captain cure his seasickness.You'll be rewarded with HM1,Cut.Use this technique to get to the gym.
Now,go back to Cerulean City.Use Cut to get rid of the bush blocking Rock Tunnel.Go through Rock Tunnel to get to Lavender Town.Use Lavender Town's Underground Tunnel to go to Celadon City.Go to the big department store and buy a drink.Give it to the guard blocking Saffron City.He'll let you through.Team Rocket has taken over Silph Co.Stop them to get the Silph Scope,which allows you to see ghosts.Use this item to beat Team Rocket in Lavender Town.
Go to Celadon City again.Team Rocket has taken over that one as well.Beat them again to get the Master Ball,the best ball for capturing Pokemon ever.Now,you can go to the gym and get a badge.You should go to Saffron City and get Sabrina's badge as well.Then,you should go to the Fighting Dojo.Beat the trainers to get your pick of 2 rare Fighting type Pokemon.
Next,head down to Fushcia City.Go to the Safari Zone and find the Warden's teeth.Give it to him and get rewarded with HM4,Surf.Surf allows you to go in water.Then,beat the gym leader to get a badge.
Now,surf down to Seafoam Islands.Get through it and continue surfing down to Cinnabar Island.Go to the Burned Lab to find the Secret Key.Use the key to open the door to the gym.
Now,fly to Viridian City.The gym leader will be back.Battle and defeat him to get your final badge.Now you're on your way to the Pokemon League!
Go through the front gate.Continue on until you come to a cave.That cave is Victory Road.Go through it to make it to the Pokemon Headquarters.Go up the steps to face the Elite 4.
After you beat them,go to the Unknown Dungeon.The person blocking the entrance will be gone.You'll finally be able to capture Mewtwo!